Power storage systems having a flywheel that is charged by a driving object and subsequently serves as source of power for, e. g., an electric motor is used, inter alia, in driving systems such as a driveline of a vehicle. However, known systems are limited, the energy storage capacity is limited by many factors such as the weight of the system, security requirements, the availability of suitable materials as well as the availability of suitable driving systems for the recharging of the flywheel and for the discharging of the same. In a driveline in a hybrid vehicle, an energy storage is found, which, e.g., may be a battery and/or a fuel tank, an electric drive motor and/or an internal combustion engine.
To be able to make use of the energy at retardation of a vehicle, for instance an automobile or a train, a fast system that manages to transmit and store high powers is required. The stronger the retardation is, the higher power the system has to be able to handle in order to make use of the energy.
A known system for storage of kinetic energy is shown in U.S. Pat. No. 5,931,249. The system described according to the document comprises a flywheel, intended for accumulation and discharging of energy, respectively, which is coupled to an electric apparatus operating as motor and generator, respectively, depending on whether energy is fed to or from the flywheel. When the system is used in a vehicle, during shorter periods of time the vehicle may be driven from the flywheel. The flywheel rotates at a high speed in vacuum. Together with the system described, high currents are required, which results in high losses if high power is to be handled. Thus, the known system is not suitable for high powers.
Today's batteries are limited in respect of the power that they manage to carry. This entails that the charging time for battery-powered vehicles generally amounts to several hours. A battery-powered vehicle cannot be driven more than a limited range before the vehicle has to be brought to a recharging station and there be recharged during a relatively long time before the vehicle again has a certain range, frequently in the range of 100 km.